Effect of Nano-SiC on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy Processed by Thixomolding

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Magnesium injection molding technology was used to produce Mg based nanocomposites. AZ91 chips were mixed with 5 wt.% of β-SiC nanoparticles in solid state and fed to pre-heated cylinder of prototype injection molding machine. Using screw rotation, granules were transferred to nozzle area at simultaneous intensive shearing and mixing of slurry containing reinforcement phases. Injection process was conducted at 595 °C, which corresponded to about 90% liquid phase and cast to steel die preheated to 150 °C. Detailed characterization of microstructure was performed using SEM and TEM microscopes. Composite microstructure consisted of α(Mg) globular grains with size of about 60 μm and volume of 7-10% surrounded by mixture of proeutectic magnesium solid solution with irregular shape and average size of 12 μm as well as fine eutectic mixture (α(Mg) + β-Mg17Al12). Additionally, TEM-BF image showed β-SiC nanoparticles with size of 20-50 nm in the area of eutectic. Hardness and compression strength of AZ91 nanocomposites increased from 58 to 75 HV and from 200 to 235 MPa, respectively.

Abstract: The effect of Cd and Sb addition on the microstructural and mechanical properties of as-cast AZ31 alloys was investigated and compared. The results indicate that the difference of Sb and Cd in the microstructure and mechanical properties of as-cast AZ31 magnesium alloy is significant. Addition of 0.15%Sb (mass fraction) to AZ31 alloy can refine the matrix and β-Mg17Al12 phase but not form a new phase Mg3Sb2. Oppositely, by addition of 0.3-0.7% Cd to AZ31 alloy, Cd was dissolved into the AZ31 alloy, the phase composition did not change but was refined also. Accordingly, the Cd-refined AZ31 alloy exhibits higher tensile and impact toughness and Brinell hardness properties than the Sb- refined one. The difference of Sb and Cd in the mechanical properties is possibly related to the solid solution of Cd into the matrix and formation of Mg3Sb2 which has the same close-packed hexagonal structure as α-Mg.

Abstract: The effect of Gd(gadolinium) on the microstructure and mechanical properties of aged AZ81 magnesium alloy were investigated. The results showed that 2wt.%Gd addition results in the obvious refinement of grain size, the decrease of β-Mg17Al12 phase and the formation of Al2Gd phase, and improves the mechanical properties of AZ81 alloy at room and high temperature. After the addition of 2wt.%Gd, the tensile strengths are enhanced from 203.2MPa to 249.3MPa at room temperature and from 157.2MPa to 197.3MPa at 150°C. Meanwhile, the elongations are increased.

Abstract: AZ80 magnesium alloys were deformed at different temperature (270°C, 300°Cand 330°C)with different deformation ratio from 10% to 50%. The influence of varying the deformation temperature and ratio on the microstructure and hardness of AZ80 magnesium alloy was studied. The experimental results show that the hardness increased with the increasing of deformation and the hardness is up to the peak value with 40% deformation at 300°C. The microstructure was homogeneous and the grain was refined after hot deformation.The roles of both deformation strengthening and dispersition strengthening were to im prove the mechanical property of AZ80 magnesium alloy.

Abstract: The effect of low content of Ca （0.9 or less）on the microstructure and mechanical properties of AZ63 alloys were studied in this paper. The results show that, adding a small amount of Ca , the alloy does not generate Al2Ca phase. The calcium dissolved into the matrix or compound phase and have an uneven distribution, but it can improve the distribution of β-Mg17Al12 phase ,refine the grain and improve the mechanical properties. Adding 0.3%Ca to AZ63 (WT%), the microstructure and mechanical properties of alloy are more ideal.

Abstract: Subscript text Nd can obviously improve the mechanical properties of spray deposited 1%Nd, 2%Nd extruded and heat treatment alloy. Nd solid solution in α-Mg matrix lead to the hardness of 2%Nd spray deposited magnesium alloy extruded is higher than that of after heat treatment. A large number of Al2Nd particles precipitation is the key factor to the highest hardness value(139.4Hv) in 2%Nd magnesium alloy after 370°C/3h+205°C/24h heat treatment. Moreover, the precipitation of Al2Nd accompany with Al2Ca and Al-Mn phase increased.